1.Field of the Invention
The present invention relates to a method of manufacturing an electronic device used for electronic and communication equipment such as portable communication equipment and an electronic computer.
2.Description of Related Art
Conventionally, electronic devices containing piezoelectric oscillation elements such as surface acoustic wave elements and crystal oscillation elements (electronic devices with built-in piezoelectric oscillation elements) have been used for electronic and communication equipment such as portable communication equipment and electronic computers.
As such electronic devices, a “crystal oscillator” which is the electronic device containing the crystal oscillation element will be described by way of example.
The conventional crystal oscillator has an insulating base 21 constructed by laminating plate-shaped insulating layers 21a and 21b and a frame-shaped insulating layer 21c, as illustrated in FIG. 23, for example. An area on an upper surface of the plate-shaped insulating layer 21b and surrounded by the frame-shaped insulating layer 21c is provided with a pair of connecting pads 22. A crystal oscillation element 25 having a pair of oscillation electrodes electrically connected through conductive adhesives is attached to the connecting pads 22. A cover 27 made of a metal is joined to the top of the frame-shaped insulating layer 21c through a wax material, thereby air-tightly sealing a space where the crystal oscillation element 25 is carried (see JP2001-274649-A, for example).
Such a crystal oscillator is set into thickness sliding oscillation at a predetermined frequency corresponding to the characteristics of the crystal oscillation element 25 when a varied voltage from the outside is applied between the oscillation electrodes of the crystal oscillation element 25 through an input/output terminal 23 provided on a lower surface of the insulating base 21. A reference signal having a predetermined frequency is oscillated and outputted by an external oscillation circuit on the basis of the resonance frequency. Such a reference signal is utilized as a clock signal in the electronic and communication equipment such as the portable communication equipment, for example.
The insulating base 21 in the above-mentioned crystal oscillator is generally formed by dividing a large-sized master substrate to obtain pieces. The crystal oscillation element 25 is attached to each of the obtained pieces (the insulating base 21), and the cover 27 is joined to the top of the frame-shaped insulating layer 21c, thereby manufacturing the crystal oscillator.
The cover 27 in the above-mentioned crystal oscillator is cut down by dividing a large-sized metal plate (a main cover), similarly to the insulating base 21.
The cover 27 is electrically connected to a ground terminal through the insulating base 21. When the crystal oscillator is used, the cover 27 is held at a ground potential so that noise from the outside is shielded.
The space where the crystal oscillation element 25 is carried may be air-tightly sealed by attaching a seal ring made of a metal so as to surround the crystal oscillation element 25 in place of the frame-shaped insulating layer 21c and joining the cover 27 made of a metal to the top of the seal ring by seam welding or the like.
In the above-mentioned conventional crystal oscillator, however, it is necessary to divide the large-sized master substrate to obtain the individual insulating bases 21 and divide a large-sized main cover to obtain the individual covers 27 prior to the assembling thereof so that the two types of members are respectively obtained by separate dividing steps.
Consequently, the assembling steps of the crystal oscillator become complicated, which does not improve productivity.
When the crystal oscillator is assembled after preparing the individual insulating bases 21 and the individual covers 27 in advance, as described above, each of the plurality of insulating bases 21 must be held in a carrier in order to perform work for the assembling.
Furthermore, the cover 27 is positioned and mounted on the individual insulating base 21 held in the carrier, so that the assembling steps for the crystal oscillator become complicated.